Downsizing of supermassive black holes from the SDSS quasar survey - II. Extension to z ∼ 4

Starting from the quasar sample of the Sloan Digital Sky Survey (SDSS) for which the C IV line is observed, we use an analysis scheme to derive the z-dependence of the maximum mass of active black holes, which overcomes the problems related to the Malmquist bias. The same procedure is applied to the low-redshift sample of SDSS quasars for which H beta measurements are available. Combining with the results from the previously studied MgII sample, we find that the maximum mass of the quasar population increases as (1 + z)(1.64 perpendicular to 0.04) in the redshift range 0.1 (sic) z (sic) 4, which includes the epoch of maximum quasar activity.